1,6,7,8-Tetrahydro-4-oxo-4H-pyrido {8 1,2-A{9 pyrimidine-9-carboalkoxy compounds

ABSTRACT

Compounds having the structure   OR A PHARMACEUTICALLY ACCEPTABLE SALT THEREOF, WHEREIN R1 is alkyl or aryl; R2 is hydrogen or alkyl; R3 is hydrogen, halogen, alkyl, or aryl; and R4 is alkyl, have useful antidepressant activity.

United States Patent [191 Yale et al.

[451 Aug. 5, 1975 I,6,7,S-TETRAHYDRO-4-OXO-4H-PYRIDO l ,2-A]PYRIMIDINE-9-CARBOALKOXY COMPOUNDS [75 Inventors: Harry L. Yale, New Brunswick;

Ervin R. Spitzmiller, Edison, both of NJ.

[73] Assignee: E. R. Squibb & Sons, Inc.,

Princeton, NJ.

[22] Filed: Sept. 9, 1974 [21] App]. No.: 504,011

[52] US. Cl 260/251 A; 260/295 R; 260/471 A; 260/473 R; 260/476 R; 260/482 R; 260/483;

424/25! [51] Int. Cl. A61K 31/505; CO7D 471/04 [58] Field of Search 260/251 A [56] References Cited OTHER PUBLICATIONS Antaki, J. Org. Chem. 27, 1371-1374 (1962).

[57] ABSTRACT Compounds having the structure or a pharmaceutically acceptable salt thereof, wherein R is alkyl or aryl; R is hydrogen or alkyl; R;, is hydrogen, halogemalkyl. or aryl; and R is alkyl, have useful antidepressant activity.

'9 Claims, No Drawings l ,6 ,7 ,8-T ETRAHYDRO-4-OXO-4H-PYRIDO [1,2-A]PYRIMIDINE-9-CARBOALKOXY COMPOUNDS BRIEF DESCRIPTION OF THE INVENTION Compounds having the structure l l R "O H N R1 R N and the pharmaceutically acceptable salts thereof, are useful as antidepressants. In formula I, and throughout the specification, the symbols are as defined below.

R is alkyl or aryl;

R is hydrogen or alkyl;

R is hydrogen, halogen, alkyl, or aryl; and

R is alkyl.

The term alkyl, as used throughout the specification, refers to straight or branched chain alkyl groups having I to 6 carbon atoms. Alkyl groups having I to 3 carbon atoms are preferred.

The term alkoxy, as used throughout the specification, refers to a group having the formula YO- wherein Y is alkyl as defined above. Alkoxy groups having 1 to 3 carbon atoms are preferred.

The term halogen, as used throughout the specification, refers to fluorine, chlorine, bromine and iodine; chlorine and bromine are the preferred halogens.

The term aryl, as used throughout the specification, refers to phenyl or phenyl substituted with one or two substituents selected from alkyl, alkoxy, halogen, and trifluoromethyl.

DETAILED DESCRIPTION OF THE INVENTION The l,6,7,8-tetrahydro-4-oxo-4I-l-pyrido[ l,2-a]- pyrimidine-9-carboalkoxy compounds of formula I can be prepared from compounds having the structure I ll RC('IHOOR5 wherein R is an alkyl group having I to 3 carbon atoms. Reaction of a compound of formula II with a 2- aminonicotinic acid having the structure Ill 0 ll C-OH N NH 2 yields the corresponding pyrido[ l,2-a]pyrimidin-4-one having the structure ll HO-C The reaction is run in an aromatic solvent such as xylene or diethylbenzene, at elevated temperatures, preferably C to C. Depending of course on the particular reactants, and the temperature of the reaction, the reaction will take from I to 4 days. This procedure is not applicable when R is phenyl substituted with iodine because of the difficulty in preparing the appropriate aminocinnamate.

The carboxylicacid intermediate of formula IV can be esterified using procedures well known in the art. Reaction of a carboxylic acid of formula IV with an alkanol having the formula VI R OH yields the corresponding ester having the structure VII 0 ll R .O-C

Catalytic reduction of a compound of formula VII yields the novel compounds of formula I. The reduction reaction can be run using hydrogen gas at a pressure of from 15 psig to 75 psig. While the reaction can be run at a temperature of from 15C to 50C, it is most conveniently run at room temperature. The catalyst used is preferably Raney nickel.

The compounds of formula II are known, and can be readily prepared by reacting an acid chloride having the structure with a carboxylic acid ester having the structure wherein X is chlorine or bromine, cyanoacetate having the structure with a la]pyrimidine-9-carboalkoxy compounds of this invention can be converted, using procedures well known in the art, into their pharmaceutically acceptable acidaddition salts. Illustrative of the salts contemplated for use in this invention are the hydrohalides (e.g., the hydrochloride and hydrobrornide), sulfate, nitrate, tartrate, phosphate, maleate, fumarate, citrate, succinate, methanesulfonate, benzenesulfonate, toluenesulfonate, and the like.

The compounds of formula I, and the pharmaceutically acceptable salts thereof, are useful for relieving depression (particularly endogenous depression) in mammals, in a manner similar to imipramine, when administered in a daily dose of from 0.5 mg/kg to 3 mg/kg, preferably 1 mg/kg to 2 mg/kg.

The compounds of the present invention can be administered orally in the form of tablets, troches, capsules, elixirs, suspensions, syrups, wafers, chewing gum, and the like. Such compositions and preparations should contain at least 0.1% of active compound. The percentage in the compositions and preparations can, of course, be varied and can conveniently be between about 5 to about 75 percent or more of the weight of the unit. Preferred compositions according to the present invention are prepared so that an oral dosage unit form contains between about 5 and 250 milligrams of active compound.

The following examples are specific embodiments of this invention.

, EXAMPLE 1 1,6,7,8-Tetrahydro-2-methyl-4 oxo-4H-pyrido-[ 1,2-

a]pyrimidine-9-carboxylic acid, methyl ester a A. 2-Methyl-4-oxo-4H-pyrido[ 1,2-a]pyrimidine-9- carboxylic acid 2-Aminonicotinic acid (13.8 g, 0.1 mole), methyl acetoacetate (23.2 g, 0.2 mole), and p toluenesulfonic acid (0.5 g) are stirred and heated under reflux conditions for 72 hours in ml of ethylene glycol monomethyl ether. The mixture is filtered while still hot; the. insoluble material is unchanged 2-aminonicotinic acid. The filtrate, on cooling, deposits a crystalline solid.. This is filtered and air-dried to give 33 grams of material, melting point 220221C, dec. The insoluble ma-l terial, the filtrate from the 3.3 g and an additional 0.5 g of p-toluenesulfonic acid is stirred and heated under reflux for 24 hours to give 2.1 g of material, melting point 220221C, dec. The 3.3 g and 2.1 g are combined and heated with 450 ml of toluene under reflux conditions, and the mixture is filtered while still hot to remove an additional 1.1 g of unreacted 2- aminonicotinic acid. The filtrate yields 3.3 g of the title compound, melting point 233235C, dec.

B. 2-Methyl-4-oxo-4H- pyrido[ l ,2-a]pyrimidine- 9-carboxylic acid, methyl ester A suspension of 2-rnethyl-4 -oxo-4H-pyrido[1,2-a]- pyrimidine-9-carboxylic acid (7 g, 0.034 mole) in a SO-i lution of sulfuric acid (3.5 g, 0.035 mole) in 700 ml of; absolute methanol is heated with stirring under reflux conditions to achieve solution. The reaction mixture is. maintained at reflux for 48 hours. The acidic solution is cooled to room temperature and sodium bicarbonate (6.3 g, 0.07 mole) is added. After stirring for 2 hours, a 50% aqueous solution of a sample of the reaction mixture has a pH of 7.2. The solvent is removed by concentration on a rotary evaporator. The solid residue is extracted twice with 250 ml portions of ether. The ether extracts are combined and the solvent removed by distillation. Recrystallization of the residue (6.5 g)

from 200 ml of diisopropyl ether yields 4.4 g of the title compound, melting point 7577C.

C. 1,6,7,8-Tetrahydro-2-methyl-4-oxo-4H-pyrido[ l ,2-a]- pyrimidine-9-carboxylic acid, methyl ester 2-Methyl-4-oxo-4H-pyrido[ 1,2-a]pyrimidine-9- carboxylic acid, methyl ester (22 g, 0.01 mole) is dissolved in 200 ml absolute ethanol and 3 g of pyrophoric Raney nickel is added. The solution is treated with hydrogen at 50 psi at room temperature in a Parr pressure vessel. After 15 minutes, 0.02 mole of hydrogen is absorbed. The catalyst is removed by filtration and the filtrate is concentrated on a rotary evaporator. The residue (2 g) has a melting point of l20l22C. Recrystallization from ml of diisopropyl ether yields 1.55 of the title compound, melting point 126128C.

EXAMPLES 2 TO 10 Following the procedure of Example 1, but substituting the compound shown in column 1 for methyl acetoacetate and the compound shown in column II for; 2-

aminonicotinic acid, the compound shown in column III is obtained.

What is claimed is: l. A compound having the structure ll R -O-C H N R 2. A compound in accordance with claim 1 wherein R is alkyl.

3. A compound in accordance with claim 1 wherein R is phenyl.

4. A compound in accordance with claim 1 wherein R 'is phenyl substituted with one or two alkyl, alkoxy, halogen or trifluoromethyl groups.

5. A compound in accordance with claim 1 wherein R is hydrogen.

6. A compound in accordance with claim 1 wherein R is alkyl.

7. A compound in accordance with claim 2 wherein R is hydrogen.

8. A compound in accordance with claim 1 wherein R is hydrogen.

9. The compound in accordance with claim 1 having the name l,6,7,8-tetrahydro-2-methyl-4-oxo-4H- pyrido[ l,2-a]-pyrimidine-9-carboxylic acid, methyl ester. 

1. A COMPOUND HAVING THE STRUCTURE
 2. A compound in accordance with claim 1 wherein R1 is alkyl.
 3. A compound in accordance with claim 1 wherein R1 is phenyl.
 4. A compound in accordance with claim 1 wherein R1 is phenyl substituted with one or two alkyl, alkoxy, halogen or trifluoromethyl groups.
 5. A compound in accordance with claim 1 wherein R2 is hydrogen.
 6. A compound in accordance with claim 1 wherein R2 is alkyl.
 7. A compound in accordance with claim 2 wherein R2 is hydrogen.
 8. A compound in accordance with claim 1 wherein R3 is hydrogen.
 9. The compound in accordance with claim 1 having the name 1,6, 7,8-tetrahydro-2-methyl-4-oxo-4H-pyrido(1,2-a)-pyrimidine-9-carboxylic acid, methyl ester. 